The bus had 25 children onboard and was picking up two more children for school around 7:48 a.m. at 106th Street and Calhoun Avenue when shots rang out, Chicago Police Department News Affairs Officer Laura Kubiak told NBC News.

Kubiak said a bullet entered the bus through a passenger side window, shattered the glass as it went through a seat and exited through the driver's side window.

The school bus was headed to Our Lady of Guadalupe School at 9050 S. Burley Ave. when it was struck by what appeared to be a bullet, according to Ryan Blackburn from the Archdiocese of Chicago’s Officer of Catholic Schools. The incident happened about two miles from the school.

"Gratefully none of the students were harmed, and this incident demonstrates why the school's mission is so critical to its families," Blackburn told The Chicago Tribune. "Teaching our students to learn well and live as disciples of Jesus Christ is what we do, and any action that threatens our children's safety cannot be tolerated."

The bus driver told investigators he didn't know what had hit the bus, and drove the bus to the school, Kubiak said.